Apparatus for measuring DC leakage current and method of use

ABSTRACT

An apparatus and method measures and analyzes DC current passing through a substantially insulating member or dielectric material that is electrically connected to, or otherwise conductive, between an energized DC electrical transmission line and an Earth potential or ground. An apparatus may utilize a DC current measuring device, a DC voltage level selection switch, a DC display, a graphical display of momentary leakage current, and an audio speaker. A process may entail extending a substantially insulating member or dielectric material between an energized DC electrical transmission line and an Earth potential, detecting a DC momentary leakage current, using a DC momentary leakage current meter to measure DC current through the member or material, and a computer to analyze and compare the DC current, and deliver results or a warning that the DC current has reached a threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/170,554 filed on Jun. 3, 2015, and entitled Direct Current Meter AndMethod Of Use.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

This invention relates to a Direct Current (DC) meter and method of useon energized DC electrical transmission and distribution power lines.

BACKGROUND OF THE INVENTION

This section provides background information related to the presentdisclosure which is not necessarily prior art. Certain barehand orcommon potential methods of servicing live, or energized, alternatingcurrent (AC) power lines are generally known to specially-trained orskilled individuals within the electrical construction and maintenanceindustry. Generally, barehand and common potential maintenance methodspermit maintenance on power lines to be more efficient becauseelectrical power does not need to be shut off to, or routed around, thepower line for which maintenance is to be performed. In one instance ofperforming maintenance on a high voltage AC power line, an aerial liftplatform, such as a bucket truck, may be equipped with an insulated,extendable boom to insulate workers in the bucket from ground potentialand thus any potential difference with a high voltage AC power line,with which the workers may be in common potential. In conjunction withbarehand and common potential methods used on AC power lines, an ACmeter may be used to monitor current that passes through the insulated,extendable boom. While using such a meter and method on an AC power linehas proven satisfactory, because Direct Current (DC) high voltage andassociated current behaves much differently, and an AC meter andtechniques are not satisfactory for work on a DC high voltage powerline, a new DC meter and method of using the DC meter are desired.

SUMMARY

An apparatus for measuring Direct Current (DC) from an energized DCelectrical power line may utilize a DC current measuring device tomeasure a DC leakage current from the energized DC electrical powerline, a DC numerical display that displays the DC leakage currentmeasured by the DC current measuring device, and an audio speaker thatsounds upon the DC current measuring device measuring a threshold DCleakage current value. An apparatus may further utilize in somecombination, a manual DC voltage class selector switch that is manuallyadjustable to coincide with a DC voltage of the DC electrical powerline, an automatic DC voltage class selector switch that automaticallyswitches to coincide with a DC voltage of the DC electrical power line,a graphical display that visually depicts a level of the DC leakagecurrent measured by the DC current measuring device, an aerial workplatform for containing and delivering human workers to a height of anenergized DC electrical power line, a chassis, such as a crane chassis,bucket truck chassis, trailer or other chassis. The apparatus may alsoemploy an elongate electrically insulating member having an insulatingmember first end and an insulating member second end, the insulatingmember first end connected (e.g. electrically) to the chassis, and theinsulating member second end connected (e.g. electrically) to the aerialwork platform, a conductive lead having a conductive lead first end anda conductive lead second end, the conductive lead first end contactingthe energized DC voltage transmission line, and the conductive leadsecond end contacting the aerial work platform. A corona ring may beattached proximate to the insulating member first end with an exteriorcollector band attached proximate the insulating member second end. Aninternal collector band may be attached proximate to the insulatingmember second end. A DC input lead having a DC input lead first end anda DC input lead second end may be provided with the DC input lead firstend contacting the external collector band and the internal collectorband. The DC input lead second end may be an electrical input for the DCmeasuring device. A DC ground or output lead may be provided and have aDC output lead first end and a DC output lead second end. The DC outputlead first end may be attached to an electrical ground point of the DCmeasuring device and the second end of the DC output lead may contact anEarth ground or potential. A plurality of hydraulic lines may traversean interior of the elongate insulating member. The hydraulic lines maybe electrically connected to the DC measuring device. A plurality offiber optic lines may traverse an interior of the elongate insulatingmember. The fiber optic lines may be electrically connected to the DCmeasuring device. A portable casing to be carried by an individual humanmay substantially retain the DC current measuring device, the DCnumerical display, the graphical display and the audio speaker.

The apparatus and methods of any of the present teachings, may be usedin conjunction with, or may include an energized DC electrical powerline having a voltage between 10,000 volts and 100,000 volts, inclusive,or between 100,000 volts and 200,000 volts, inclusive, or between200,000 volts and 300,000 volts, inclusive, or between 300,000 volts and400,000 volts, inclusive, or a voltage between 400,000 volts and 500,000volts, inclusive, or between 500,000 volts and 600,000 volts, inclusive.

In another example of the present teachings, a portable apparatus foruse with an energized DC transmission line may utilize a substantiallyelectrically insulating structure, a DC current measuring device tomeasure DC current passing through the substantially electricallyinsulating structure, a DC voltage level switch, a DC display to displaya DC current measured by the DC current measuring device at a DC voltagelevel of the DC voltage level switch, a graphical display to indicate anamperage of the DC current, and an audio speaker to sound at a thresholdamperage of the DC current measured by the DC current measuring device.An apparatus may further employ a casing to which the DC currentmeasuring device, the DC voltage level switch, the digital DC display,the graphical display, and the audio speaker, attach. The apparatus mayfurther exhibit a first end of the substantially electrically insulatingstructure that contacts the energized DC transmission line, and a secondend of the substantially electrically insulating structure that contactsan earth ground (i.e. ground voltage, ground potential), an electricallead having an electrical lead first end and an electrical lead secondend, with the electrical lead first end fastened proximate to the secondend of the insulating structure and the electrical lead second endfastened to the DC current measuring device. A portable apparatus mayalso employ a DC ground lead (e.g. an electrically conductive cable)having a DC ground lead first end and a DC ground lead second end, withthe DC ground lead first end attached to the DC current measuring device(e.g. an electrical ground point of the DC current measuring device),and the second end of the DC ground lead contacting an Earth ground(e.g. ground voltage or ground potential). As representative examples,the substantially electrically insulating structure may be a ladder,scaffolding, a hydraulic line, a boom (e.g. a crane boom, a bucket truckboom, or an aerial platform device boom), or nearly any fiber reinforcedplastic (“FRP”) structure used in as an electrically insulatingstructure.

In another example of the present teachings, an apparatus for use withan energized DC transmission line may utilize an electrically conductivesupporting structure of an energized DC electrical power line, anenergized DC transmission line located between a surface of Earth andthe electrically conductive supporting structure, a first elongatesubstantially electrically insulating structure contacting each of theelectrically conductive supporting structure and the energized DCtransmission line, and a DC current measuring device electrically wiredin series between the first elongate substantially electricallyinsulating structure and an electrical ground (e.g. ground potential orground voltage). A DC current measuring device may be electrically wiredin series between the first elongate substantially electricallyinsulating structure, and an electrical ground may be an electrical leadhaving an electrical lead first end and an electrical lead second end,the electrical lead first end electrically connected to the firstelongate substantially electrically insulating structure and proximateto the electrically conductive supporting structure of the energized DCelectrical power line. The electrical lead second end may be fastened tothe DC current measuring device. A DC ground lead having a DC groundlead first end and a DC ground lead second end, may have the DC groundlead first end attached to an electrical ground point of the DC currentmeasuring device, and the DC ground lead second end in contact with anEarth ground (e.g. ground potential or ground voltage). The structurehaving Earth potential or Earth ground may be the electricallyconductive supporting structure. A second elongate substantiallyelectrically insulating structure may contact each of the electricallyconductive supporting structure and the energized DC transmission line.The DC current measuring device may also be electrically connected inseries to the second elongate substantially electrically insulatingstructure.

The DC current measuring device may be electrically connected in seriesto the second elongate substantially electrically insulating structureto measure a momentary leakage current passing through both the firstelongate substantially electrically insulating structure and the secondelongate substantially electrically insulating structure, when the firstand second structures are electrically connected. The first elongatesubstantially electrically insulating structure and the second elongatesubstantially electrically insulating structure may be substantiallyparallel to each other, and may be in tension due to a weight of theenergized DC electrical power line suspended from the elongatesubstantially electrically insulating structures. The apparatus mayfurther employ a DC voltage selector switch that adjusts manually orautomatically to coincide with a DC voltage level of the energized DCelectrical power line, a DC numerical display that displays the DCcurrent measured by the DC current measuring device, an audio speakerthat sounds upon the DC current measuring device measuring a thresholdDC current value, a graphical display that visually depicts a level ofthe DC leakage current measured by the DC current measuring device, anda hand-held casing to which the DC current measuring device, the DCvoltage selection switch, the digital and graphical display, and theaudio speaker are attached or encased.

A process of the teachings of the present invention may be providing anenergized DC electrical line above an Earthen surface (i.e. a surface ofthe Earth), electrically connecting or electrically bonding asubstantially electrically insulating structure against the energized DCelectrical line and the Earthen surface (or surface with Earthpotential), providing a DC current meter, in series between theinsulating member and the Earthen surface, a DC current meter, andmeasuring a DC momentary leakage current flowing through the insulatingmember with the DC current meter. DC momentary leakage current isconsidered to be direct current that flows through, despite howrelatively minuscule or not miuscule, a substantially electricallyinsulating structure (e.g. an FRP or fiber reinforced plastic or othermaterial largely considered to be insulating). Measuring a DC momentaryleakage current that passes through the insulating member with the DCcurrent meter, may further entail measuring every 1/60^(th) or1/120^(th) of a second with the DC current meter, the DC momentaryleakage current flowing through the insulating member or substantiallyelectrically insulating structure. The process may further includestoring in a digital memory, a plurality of momentary leakage currentvalues measured by the DC current meter; and comparing the plurality ofmomentary leakage current values measured by the DC current meter to apredetermined threshold current value indicative of a DC flashovercurrent value for the substantially electrically insulating structure.Depending upon the comparison of the values, the process may also entailsounding an audible alarm when any of the plurality of momentary leakagecurrent values measured by the DC current meter is larger than thepredetermined threshold current value and activating a visible alarmwhen any of the momentary leakage current values measured by the DCcurrent meter is larger than the predetermined threshold current value.Still yet, the process may include calculating a moving average for theplurality of momentary leakage current values, comparing the movingaverage to a predetermined threshold current value indicative of a DCcurrent flashover current value for the substantially electricallyinsulating structure, and sounding an audible alarm when the movingaverage of the plurality of momentary leakage current values measured bythe DC current meter is larger than the predetermined threshold currentvalue.

In another example, a process may include providing an energized DCelectrical line above a surface of the Earth, locating a first end of asubstantially electrically insulating structure proximate (e.g. nearenough to experience circulating current or induction current, orelectrically attached with an electrically conductive jumper cable) theenergized DC electrical line, locating a second end of a substantiallyelectrically insulating structure proximate an Earthen surface,providing, in series between the insulating member and the Earthensurface, a DC current meter, and measuring a plurality of momentaryleakage current values flowing through the substantially electricallyinsulating structure using the DC current meter. The process may furtherinclude measuring every 1/60^(th) of a second (or other time interval),a DC momentary leakage current flowing through the substantiallyelectrically insulating structure using the DC current meter,calculating a moving average for the plurality of momentary leakagecurrent values, storing in a digital memory, the plurality of momentaryleakage current values measured by the DC current meter, and comparingthe plurality of momentary leakage current values measured by the DCcurrent meter to a predetermined threshold current value indicative of aDC current flashover current value for the substantially electricallyinsulating structure, and sounding an audible alarm when any of theplurality of momentary leakage current values measured by the DC currentmeter is larger than the predetermined threshold current value. Theprocess may also include activating a visible alarm when any of theplurality of momentary leakage current values flowing through thesubstantially electrically insulating structure measured by the DCcurrent meter is larger than the predetermined threshold current value.The process may further include locating a first end of a substantiallyelectrically insulating structure proximate the energized DC electricalline, electrically connecting a first end of a substantiallyelectrically insulating structure to the energized DC electrical lineand the Earthen surface. Locating a second end of a substantiallyelectrically insulating structure proximate an Earthen surface, mayfurther include locating a second end of a substantially electricallyinsulating structure proximate on a surface that has Ground potential.The process may further include calculating a moving average for theplurality of momentary leakage current values; storing in a digitalmemory, the plurality of momentary leakage current values measured bythe DC current meter, and comparing the plurality of momentary leakagecurrent values measured by the DC current meter to a predeterminedthreshold current value indicative of a DC current flashover currentvalue for the substantially electrically insulating structure.

Calculating a moving average for the plurality of momentary leakagecurrent values may further include calculating a moving average using apredetermined number of momentary leakage current values measured insuccession by the DC current meter by excluding the first momentaryleakage current value of a series of momentary leakage current valuesand including the next momentary leakage current value following animmediately prior subset of momentary leakage current values used tocalculate an average. The process may further include sounding anaudible alarm when any of the plurality of momentary leakage currentvalues measured by the DC current meter is larger than the predeterminedthreshold current value. The process may further include predictingelectrical flashover of the substantially electrically insulatingstructure from one of the momentary leakage current values that ismeasured by the DC current meter by comparing the DC momentary leakagecurrent value to a predetermined threshold value indicative of a DCcurrent flashover value of the substantially electrically insulatingstructure. The process may include displaying on a DC numerical displayof the DC current meter, the DC momentary leakage current, sounding anaudio alarm upon the DC current measuring device measuring a thresholdvalue of the DC momentary leakage current, displaying on a graphicaldisplay, the threshold value for the substantially electricallyinsulating structure, and displaying on the graphical display, the DCmomentary leakage current measured by the DC current meter. Thesubstantially electrically insulating structure may be a hydraulic line,a boom, or any such structure that is made from a fiber reinforcedplastic material or other insulating material.

In another example, a process may include measuring direct current (DC)through a material by providing a DC meter capable of measuring amperageat voltages of an electrically energized DC power line, providing anelectrically energized DC power line to supply DC through asubstantially dielectric material, measuring the DC passing through thesubstantially dielectric material to determine an instantaneous DCamperage value, comparing the instantaneous DC amperage value to a knownDC amperage flashover value for the substantially dielectric material,and activating an alarm when the instantaneous DC amperage value isequal to or greater than the known DC amperage flashover value for thesubstantially dielectric material. Measuring the DC passing through thesubstantially dielectric material to determine an instantaneous DCamperage value, may include repeatedly measuring the DC passing throughthe substantially dielectric material to create a plurality ofinstantaneous DC amperage values, and calculating a moving average usingthe plurality of instantaneous DC amperage values. Activating an alarmwhen the instantaneous DC amperage value is equal to or greater than theknown DC amperage flashover value for the substantially dielectricmaterial may further include providing a DC portable meter, anddisplaying the instantaneous DC amperage value on a visible display ofthe DC portable meter. The electrically energized DC power line may bebetween 38 kV and 600 kV, inclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefitsthereof may be acquired by referring to the follow description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic depicting internal components of a voltage meterand associated user-readable displays in accordance with teachings ofthe present invention;

FIG. 2 is a perspective external view of a voltage meter encased withina housing to contain its operative parts and promote portability;

FIG. 3 is a perspective view of a voltage meter located in an examplein-use location to monitor direct current that passes through aninsulated boom from a direct current voltage line in accordance withteachings of the present invention;

FIG. 4 is a diagram depicting components to which a voltage meter may beelectrically connected to monitor voltage in accordance with teachingsof the present invention;

FIG. 5 is a graph of DC current versus time, for a voltage class,showing DC current readings, in an example measuring scenario using thecurrent meter in accordance with teachings of the present invention;

FIG. 6 is a view of an insulating ladder arranged in contact with anenergized conductor and a voltage meter, for measuring current passagethrough the insulating ladder, in accordance with teachings of thepresent invention;

FIG. 7 is a view of insulating scaffolding arranged in contact with anenergized conductor and a voltage meter, for measuring current passagethrough the insulating scaffolding, in accordance with teachings of thepresent invention;

FIG. 8 is a view of an insulating hot stick used during a replacement ofan insulator on a power line, in accordance with teachings of thepresent invention;

FIG. 9 is an interior view of a boom showing locations of a hydraulicline collector block and a fiber optic conductive clamp; and

FIG. 10 is a flowchart of a routine controlled by software withinmicrocontroller to monitor current through an insulating body, inaccordance with teachings of the present invention.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement orarrangements of the present invention, it should be understood that theinventive features and concepts may be manifested in other arrangementsand that the scope of the invention is not limited to the embodiments orexamples described or illustrated. The scope of the invention isintended only to be set forth by the scope of the claims that follow.Each embodiment or example is provided by way of explanation of theinvention, one of many embodiments of the invention, and the followingexamples should not be read to limit, or define, the scope of theinvention.

FIG. 1 is a schematic view of components of a DC current meter 10 inaccordance with teachings of the present invention. DC current meter 10may include an electrically conductive collector 12, an analog front-end14, which is a current receiver that receives or collects current fromelectrically conductive collector 12 to be measured and used as an input26 for an analog-to-digital converter 16, also known in abbreviated formas “ADC”, whose digital output signal 28 is used as an input for amicro-controller 18, which is also a computer. With reference includingFIG. 5, multiple sources of electrical current to be used as input intothe analog front end 14 of ADC 16 may be electrical current from a boom20, electrical current from one or more of a type of hydraulic line 22,and electrical current from a leveling rod or one or more of a fiberoptic cable 24, or both a leveling rod or one or more of a fiber opticcable 24. For example, electrical lines 20 a, 20 b may carry electricalcurrent from boom 20 such that electrical line 20 a may carry currentfrom an interior surface or inside diameter surface of boom 20, andelectrical line 20 b may carry current from an exterior surface oroutside diameter surface of boom 20, as depicted, to electricallyconductive collector 12. Electrical lines 22 a, 22 b may each carryelectrical current from a single hydraulic line 22 or one or morehydraulic lines 22 to electrically conductive collector 12. Electricallines 24 a, 24 b, may each carry electrical current from fiber opticcable 24 to electrically conductive collector 12. In place of, or inadditional to fiber optic cable 24, a leveling rod may conduct and carryelectricity to electrically conductive collector 12. Although electriclines, fiber optic cables, hydraulic lines, and one or more levelingrods are used as specific examples of structures for which currentpassing through such structure may be measured, the teachings of thepresent disclosure may be employed to measure or monitor electricalcurrent for any structure, which may be an insulating structure, ifdesired.

With reference again to FIG. 1, after electrical current from each ofboom 20, hydraulic line 22, and fiber optic cable 24 passes onto or intoelectrically conductive collector 12, such electrical current may thenpass into analog front end 14. For example, electrical current from boom20 passes through electrical lines 20 a, 20 b and through a fuse 30,which is an electrical protective device to protect all electricaldownstream components from a power surge, before entering analogfront-end 14. Electrical current from one or more hydraulic lines 22 maypass through electrical lines 22 a, 22 b, and through a fuse 32, whichis an electrical protective device to protect all electrical downstreamcomponents from a power surge, before entering analog front-end 14.Electrical current from one or more fiber optic cables 24 may passthrough electrical lines 24 a, 24 b, and through a fuse 34, which is anelectrical protective device to protect all electrical downstreamcomponents from a power surge, before entering analog front-end 14.Instead of a fuse 30, 32, 34 which may be a one-time-use type of devicewhen employed for its purpose, a different device with the same currentinterrupting or stopping purpose may be substituted, such as a circuitbreaker, which may be resettable.

Analog front end 14 measures the amperage flowing from electrical inputcollector 12 which is a measurement also referred to as “leakagecurrent” because current is flowing through devices such as boom 20,hydraulic line 22, and fiber optic cable 24, which are designed andknown to be insulating devices to the extent their materials permit themto be insulating or insulative given the voltage to which boom 20,hydraulic line 22, and fiber optic cable 24 that are directly orultimately connected. Thus, any current that passes through suchotherwise insulating devices is known as “leakage current” rather thansimply current. Measuring of such leakage current is performed in analogfront end 14, which also performs an electrical continuity test on eachof any connected boom 20, hydraulic line 22, and fiber optic cable 24.Measuring current or leakage current, such as DC current, through otherdevices is possible by using the teachings of the present invention.

Analog front end 14 is an electrical circuit and may employ highprecision shunt resistors for each channel creating a path to ground.Alternatively, a Hall effect sensor can be used instead of one or moreshunt resistors. A Hall effect sensor may be arranged in any necessaryposition relative to the device from which to measure magnetic current.As an example, the Hall effect sensor may be arranged parallel to, orotherwise proximate to, a capacitor or other electric circuit component,with a lead to ground. The Hall effect sensor may be used to detect amagnetic field that translates to a current, such as direct current. Theshunt resistors are monitored by high bandwidth and high gain amplifiersfor potential difference (i.e. voltage) across them, induced by current(also known as leakage current) flowing to ground. Its resistor andamplifier design will allow for bi-directional leakage current detectionfor a scale of +/−0 to 500 microamperes or single-ended +/−0 to 1000microamperes range. The output of an amplifier may be amplified again(e.g. once more) before being input into analog to digital converter 16as input 26. The amplifier output, which is input 26, will go to analogto digital converter 16 employing a precision high-speed ADC chip.Alternatively input 26 may be directed directly to microcontroller 18and thereby bypass a separate ADC 16 if microcontroller 18 is equippedwith its own built-in ADC, which may depend upon specific applicationrequirements. The specific application requirements that may dictatewhether a separate ADC is used, or input signal 26 goes directly inmicrocontroller 18 may be the bandwidth of the input signal, and theaccuracy and precision of the detected current. The operation orfunctionality is such that leakage current passing through the internalshunt resistors from the test insulation connections of the boomequipment, will create a potential difference across the resistor withreference to ground. Any analog-to-digital converter, whether it is aseparate ADC outside of microcontroller 18 or within microcontroller 18,converts the analog voltage level to a digital representation, which canthen be processed by microcontroller 18 to perform various outputs suchas an audible trigger alarm(s) from speaker 38, a readable display on anLCD display 40, a graphical display such as a momentary leakage currentgraphical display 42, and then store or log all output or results tomemory 44, which may be an external memory device as a separatecomponent from microcontroller 18.

With continued reference to FIG. 1, other components of the teachings ofthe present invention will be explained. FIG. 1 depicts one or morefunction buttons 46. Function buttons may be input controls to controlfunctions of the microcontroller in accordance with the presentinvention. For instance, one function may be an on and off switch tosupply or electricity or power to, and prevent power or electricity fromflowing to microcontroller 18. Another function button 46 may be acontinuity test button, also known as a self-test button. Such a testwhen initiated by pressing such a button, permits the microcontroller tocause electricity to test the continuity of each of the electrical wires20 a, 20 b, 22 a, 22 b, 24 a, 24 b to ensure that no electrical opencircuits or breaks in continuity in any of the leakage currentelectrical wires 20 a, 20 b, 22 a, 22 b, 24 a, 24 b exists. Otherfunctions to invoke with a function button 46 are possible. A voltageclass selector 48 may function to permit a user to manually select avoltage class, range or upper limit at which a voltage meter, such as DCvoltage meter 10, may properly function. Alternatively, voltage classselection may be performed automatically, and internally within DCvoltage meter 10 upon DC voltage meter 10 sensing or measuring voltage.Thus, no manual voltage selection need be performed with a switch suchas voltage class selector 48. Examples of voltage classes are: from0-400 kV, 0-500 kV, and 0-600 kV. Other DC voltage classes are possible.This, in accordance with the present teachings, voltage class selector48 could have three distinct positions, or more. A ground wire 50 thatcreates an electrical path to Earth permits functions, such as testfunctions and current monitoring within microcontroller 18, andfunctioning of current meter 10 itself, to properly work.

FIG. 2 is an external view of DC current meter 10 with most of theoperative components enclosed within a casing 52. By enclosing thecomponents of DC current meter 10 within casing 52, the portability ofthe teachings of the present invention are enhanced. FIG. 2 is oneexample of how an instantaneous reading or readout, such as an LCDdisplay 40, an audio speaker 38, a voltage class selector switch 48 andan accumulated momentary leakage current graphical display 42, may bearranged or positioned within and around a surface of casing 52.

FIG. 3 depicts DC current meter 10 in an in-use position with an aeriallift device 54 equipped with a bucket 56 for human occupants. The aeriallift device 54 may be mounted to a truck, vehicle, or trailer chassis58, or similar platform, the chassis 58 may or may not have wheels. WhenDC current meter 10 is in use, a boom 20, which may be a fixed length,or extendable in a telescoping fashion, may be extended such that bucket56 resides beside an energized (i.e. live) high voltage direct currentpower line 62 so that human occupants within bucket 56 can performmaintenance on, or further construct, high voltage direct current powerline 62. When current meter 10 is in use, bucket 56, which may beconstructed with metallic components, is placed at the same potential(i.e. voltage) as DC power line 62. Similarly, a human occupant withinbucket 56 is also placed at the same potential as DC power line 62. Inorder place bucket 56 and any human occupant within the bucket 56 at thesame potential as DC power line 62, a bonding clamp 65 is used. Bondingclamp 65 provides an electrical link to bucket 56 and human occupants toachieve a common potential for the DC power line 62, bonding clamp 65and bucket 56. Bucket 56 is pivotably attached to telescoping boom 20 topermit relative motion between bucket 56 and telescoping boom 20.Telescoping boom 20 is an electrically insulating member made fromfiberglass, or fiberglass and other non-conductive materials, which mayinclude plastics and other materials.

Continuing with FIG. 3, mounted to telescoping boom 20 proximate tobucket 56 is a corona ring 64. Corona ring 64 may be mounted withinthree meters or within three yards of the junction of boom 20 and bucket56, or where most electrically advantageous. At an opposite end of boom20, proximate a truck chassis 58, other mounting platform or lowestpivot point of boom 20, an outer collector band 66 and an innercollector band 67 may be mounted to and against, an exterior and aninterior, respectively of boom 20. Boom 20 may be hollow and used as aconduit or passageway for components depicted on FIG. 4, such as one ormore hydraulic lines 22, electric lines 22 a, 22 b, and one or morefiber optic cables 24, and electric lines 24 a, 24 b. As also depictedin FIG. 4, electric lines 20 a, 20 b are attached to boom 20, and atleast electric line 20 a may traverse boom interior 60, while electricline 20 b may traverse or run along some length of an exterior surfaceor interior surface of boom 20. At a base of boom 20, an electricalcollection point exists for all structures being monitored for currentflow, which may be an input for meter 10. Each of hydraulic lines 22,fiber optic cables 24, and boom 20 are made of a dielectric material andhave electrical insulating qualities; however, even dielectric andinsulating materials will permit some relative quantity of current topass, and the teachings of the present invention including voltage meter20, are designed to detect that level of current and alert a user of theinvention.

FIG. 5 is a graph of current measurements versus time 68 in an examplemeasuring scenario using current meter 10 in accordance with teachingsof the present invention. The zones within the graph of FIG. 5 will beexplained later during a presentation of operation of the teachings ofthe present invention.

FIG. 6 depicts an insulating ladder 70 arranged in contact with anenergized electrical conductor 62 at contact points 72, 74, and acurrent meter 10 electrically connected to insulating ladder 70. At theopposite end of insulating ladder 70, a first electrically conductiveclamping ring 76 surrounds and contacts a first ladder leg 84, and asecond electrically conductive clamping ring 78 surrounds and contacts asecond ladder leg 86. A clamp ring jumper wire 80 electrically connectsto each of first electrically conductive clamping ring 76 and secondelectrically conductive clamping ring 78. Although either electricallyconductive clamping ring 76, 78 may be used, FIG. 6 depicts a meter leadin wire 82 conduct electricity from each of first electricallyconductive clamping ring 76 and second electrically conductive clampingring 78 and to current meter 10. Current meter 10 is the same currentmeter 10 depicted in FIG. 1 and FIG. 2, although in the arrangementdepicted in FIG. 6, meter lead in wire 80 is a single conductive wire.The arrangement of FIG. 6 permits current meter 10 to detect leakagecurrent passing from DC power line through the insulating ladder and toground 50.

FIG. 7 depicts another embodiment of the present teachings in which aninsulating scaffolding 82 is arranged in physical and electrical contactwith an energized DC conductor 62, such as with electrical jumper 87.When a human worker is resident upon horizontal platform 83, DC currentmeter 10 may be electrically connected to insulating scaffolding 82 tomonitor the leakage current through insulating scaffolding 82. Morespecifically, in a given horizontal plane at some distance from eitheran Earthen surface 86 upon which insulating scaffolding 82 may reside,or at some distance from energized DC conductor 62, each of verticalposts 84 passing through such horizontal plane are electricallyconnected with an electrically conductive wire 88 or multiple pieces ofelectrically conductive wire 88. Electrically conductive wire 88 may besecured against each vertical post 84 by an electrically conductiveclamp ring 90 to permit a continuous electrical loop of electricallyconductive wire 88, which securely holds electrically conductive clampring 90 and electrically conductive wire 88. Thus, a continuous loopfrom vertical pole to vertical pole around insulating scaffolding 82 iscreated. From one of electrically conductive wire 88, meter lead in wireis connected to create an electrically conductive link from electricallyconductive wire 88 to current meter 10. The arrangement of FIG. 7 willmeasure DC current passage through the insulating scaffolding and intoground via ground wire 50.

FIG. 8 depicts a first insulating hot stick 92 and a second insulatinghot stick 94 used during a replacement of an insulator 96 on a DC powerline 62, and placement of current meter 10 during use of suchreplacement, in accordance with teachings of the present invention. Ahot stick is a name used by professionals engaged in the trade ofmaintaining, constructing and reconstructing energized, or live, DCpower lines, for specific types of insulated poles, which are alsotools, and usually made of fiberglass, or fiberglass and otherinsulating material(s). The insulating materials prevent, for practicalpurposes, electrical current from traveling from DC power line 62 toground 50.

Continuing with FIG. 8, use of current meter 10 during a typicalscenario involving replacement of an aged or otherwise compromisedinsulator 96 may involve a conductor supporting structure 98, such aspart of a lattice tower or any powerline supporting structure that isgrounded and thus at the potential of ground 50 (i.e. in the industryknown as ground potential). As part of conductor supporting structure98, FIG. 8 depicts an approximately horizontal, or horizontal beam 100,with, relative to horizontal beam 100, an angled beam 102. Horizontalbeam 100 and angled beam are joined by connective structures 104 toincrease strength. With first insulating hot stick 92 and secondinsulating hot stick 94 attached to conductor supporting structure 98,such as to horizontal beam 100, first insulating hot stick 92 and secondinsulating hot stick 94 hang to the same or approximately the samelength as insulator 96. First insulating hot stick 92 and secondinsulating hot stick 94 may be separated at a specified distance by alimiting bracket 104. Each of first insulating hot stick 92 and a secondinsulating hot stick 94 is affixed to energized DC power line 62 byclamping or some suitable device, and similarly each of first insulatinghot stick 92 and a second insulating hot stick 94 is affixed tohorizontal beam 100 by clamping or some suitable device. Limitingbracket 104 may be located proximate energized DC power line 62. Whenfirst insulating hot stick 92 and second insulating hot stick 94 are inplace as depicted in FIG. 8, insulator 96 may be removed and instead ofinsulator 96, before removal, bearing the tensile load due to gravity ofenergized DC power line 62, each of first insulating hot stick 92 andsecond insulating hot stick 94 bears half the tensile load of energizedDC power line 62.

In accordance with the present invention, FIG. 8 also depicts currentmeter 10 affixed in some fashion to conductor supporting structure 98.Additionally, an electrically conductive jumper 106 located betweenfirst insulating hot stick 92 and second insulating hot stick 94,creates an electrical path between the two sticks 92, 94. Electricallyconductive jumper 106 is securely fastened to each of first insulatinghot stick 92 and second insulating hot stick 94 by an electricallyconductive clamp 108 that is consistent to each junction. From one ofelectrically conductive clamp 108 to current meter 10, a meterelectrical lead wire 110 permits leakage current to flow to currentmeter 10. A conductive ground lead 112, clamped to conductor supportingstructure 98 with clamp 114, completes an electrical current path viaconductor supporting structure 98 to Earth ground 50.

FIG. 9 is a perspective view of how hydraulic lines 22 and fiber opticcables 24 may reside within boom 20. Additionally, FIG. 9 shows howelectric lines 22 a, 22 b, 24 a, 24 b may conduct current which isdirected to meter 10 as part of the monitoring of any leakage current inaccordance with teachings of the present invention. Collector block 23is electrically conductive and may be the transition point at whichhydraulic lines 22 transition from their needing to be insulating partto not needing to be an electrically insulating part. Collector block 23is electrically conductive and may be the transition point at whichfiber optic lines 24 transition from their needing to be an electricallyinsulating part to not needing to be a an electrically insulating part.FIG. 9 also depicts fiber optic cables 24, which may be gathered with anelectrically conductive clamp 25 from which electric lines 24 a, 24 btransmit current to meter 10. Electrically conductive clamp 25 has dualelectric lines 24 a, 24 b running from it for the same reason thathydraulic collector block 23 has dual electric lines 22 a, 22 b runningfrom it, which is to easily permit an electrical continuity test frommeter 10 (e.g. as another FIG. 1 function button 46) to ensure there areno breaks or interruptions in the electrical continuity of such anelectrical circuit.

During one example operation of the present invention, and with initialreference to FIG. 3, when bucket 56 of aerial lift device 54 iselectrically bonded to energized DC power line 62, with bonding clamp65, also a conductive lead, contacting each of energized DC power line62 and bucket 56, bucket 56 and any human occupants will reach the samepotential or voltage as energized DC power line 62. With such anenergized arrangement, DC current passing through boom 20, DC currentpassing through hydraulic lines 22, and DC current passing through fiberoptic cables 24, which individually and collectively are referred to as“leakage current” must be monitored as it moves through these structuresto ground 50. Current meter 10 will monitor this DC leakage current, asdepicted in FIG. 5. FIG. 5, which is an example graph of DC current inmicroamps versus microseconds, shows leakage current measurements withina specific DC voltage class. DC current measurements may be taken ormeasured at almost any frequency, such as from 10 measurements persecond to 1000 or more measurements per second, and as previouslystated, within a particular DC voltage class for a particular energizedDC power line 62. All current measurements may be performed bymicrocontroller 18, or an average current calculated after apredetermined number of measurements, such as after 100 or 1000, or someother quantity, and then stored in a memory such as external memory 44.An average of some quantity of the current measurements may be displayedon graphical display 42, which may be a color display, and on an LCDdisplay 40, which may be a numerical display. Because over time,electrical charge may build on insulating components such as boom 20,hydraulic lines 22 and fiber optic cables 24, and as a result, anaverage current value for the total of current measurements, or somepredetermined quantity of current measurement values, may increase froma first or safe current zone 116 to current zone 118, which may be acaution zone. In caution zone 118, some current measurement values, suchas current measurement value 120 are greater than others, such ascurrent measurement value 122. Zone 124 of FIG. 5 depicts a zone ofhighest current measurement values, which are also know as currentspikes and may indicate an instance of, or impending, flash-over. Aflashover is an event in which the DC leakage current exceeds thehighest permissible value for a particular voltage class.

With continued reference to FIG. 5, zone 124 represents an impermissiblezone within which if DC leakage current reaches for a particular voltageclass or range, some intervention or preventive steps need to be takento stop or reduce the amount of leakage current passing to ground 50.Within impermissible zone 124, microamp levels for current measurements126, 128 and 130 represent the highest levels of leakage current.

A graph such as the graph depicted with FIG. 5, could be plotted formany different pieces of insulating equipment for which leakage currentneeds to be monitored. For example, as depicted in FIG. 6, the leakagecurrent passing through insulating ladder 70 could be monitored andplotted for a selected voltage class of an energized DC power line 62 ifinsulating ladder 70 is in contact with energized DC power line 62.Similarly, as depicted in FIG. 7, the leakage current passing throughinsulating scaffolding could be monitored and plotted for a selectedvoltage class of an energized DC power line 62 with which insulatingscaffolding 82 is in contact.

Alternatively, an array of information could be compiled and stored,such as in a database in memory 44 of meter 10. An array of informationmay include columns of information including, but not limited to, time(e.g. seconds), amperage reading (e.g. micro amps) at a time interval(e.g. every 1/60 of a second, every 1/100^(th) of a second, every1/120^(th) of a second), and average amperage value for a predeterminednumber of amperage readings (e.g. every 60 reading, every 100 readings),or over a predetermined time period (e.g. every second, every tenseconds). As an example, an average amperage value for a predeterminednumber of amperage readings, or an average amperage value over apredetermined time period may be displayed on LCD display 40 or otherdisplay, such as display 42, on meter 10 for visual inspection by vieweror user of meter 10. Still yet, instead of displaying a numerical valueon a display, a graphical representation may simultaneously be displayedor instead be displayed. A graphical representation may be acontinuously changing bar graph that graphically displays an averageamperage value for a predetermined number of amperage readings, or anaverage amperage value over a predetermined time period.

Before presenting details of a process or routine that meter 10, andmore specifically microcontroller 18 within meter 10, may employ inaccordance with the present teachings, further details on measurement bymeter 10 of direct current will be presented. When a fully insulatingbody is exposed to a voltage source (e.g. either AC or DC) no currentwill pass through it regardless of the voltage or potential differenceexperienced by the insulating body. However, in reality a fullyinsulating body or “perfect insulator” does not exist, and allinsulators to some degree respond or perform as resistors and thereforeare subject to Ohms law for current passing through the insulating body.This is known as resistive current. Thus, in the present teachings,resistive current is passing through the insulating body, such asinsulating boom 20, insulating ladder 70, hot sticks 92, 94, etc. towhich meter 10 is connected. In addition to resistive current passingthrough such insulating bodies, another type of current passes throughthe insulating bodies. This current is known as capacitive current.

A capacitor in its simplest form is essentially two conductive objectsseparated by an electrically insulating medium. When DC voltage isapplied to one of the conductive objects no current will flow from oneobject to the other, if the insulating medium is perfectly insulating.Regarding AC voltage (time varying voltage), when voltage is applied tothe same capacitor, a displacement current passes through thenon-perfectly insulating medium. This “capacitive” effect actuallyoccurs when DC voltage is applied as well and is known as a transientvoltage and is a result of the lack of a perfect insulator between theconductive objects and the presence of charge carriers in same. Current,known as momentary current, will flow for a short period of time andthen stop as the electrical charge between the energized source and theinsulating medium reach parity. However this electrical charge isreleased when this current flows to ground and the cycle repeats.Comparing the preceding explanation to teachings of the presentdisclosure, a boom 20 of a bucket truck, or other live line tool such asan insulating ladder 70 is an electrically insulating medium. Conductiveobjects may be DC power line 62 and ground 50, such as Earth.

With reference to FIG. 3, when bucket 56 is electrically bonded (i.e. atthe same electrical potential) to DC power line 62, boom 20, because itis physically connected to bucket 56, will still experience a very smallcurrent flow to ground 50. The current flow is the sum of the capacitiveand resistive currents explained above. The sum of these two types ofcurrent is greater with insulating devices, such as boom 20, used inconjunction with AC voltage/AC current power lines than with DCvoltage/DC current power lines. Moreover, measuring DC current, such aswith meter 10, is different than measuring AC current, especially whenDC voltages range from 70 kV to 500 KV, which may be measured withteachings of the present disclosure. As discovered during testing inconjunction with the present teachings, in direct current situations asthe electrical resistance of some insulating materials of insulatorsbegins to degrade or lose their insulating properties, either fromcontamination or when the voltage applied across an insulator increasesrelative to the resistance of the insulator, the resistive current willremain relatively unchanged. However, during this time of relativelyconsistent resistive current, “pulses” or “momentary current spikes” or“short duration spikes,” which are increases of capacitive current,which may be many orders of magnitude greater than the relatively stableresistive current, will begin to move through the insulator withincreasing intensity and frequency as the resistive threshold (i.e.breakdown) of the insulator is approached. These “pulses” of current maylast for only a few milliseconds as they discharge to ground andtherefore must be measured in small time intervals by equipmentsensitive enough to detect and monitor any pulses. Traditional analogmeters or any presently known current measuring devices that displaymeasured current are insufficient at least because an analog needle willnot react quickly enough to notify one of impending dielectricbreakdown, and a digital LCD display will not register the measuredcurrent value and display it for a long enough period of time to be ofbenefit to a user. Regardless, voltages in the DC voltage range from 70kV to 500 KV are extraordinarily high for known meters and propernotification of a dielectric failure.

Thus, teachings of the present disclosure may employ an analog todigital converter 16 or other device within meter 10 that is capable ofdetecting short-lasting current changes for a predetermined number oftimes in a minute, detecting what that current is, detecting how longeach current change or increase lasts, recording them, and displayingsuch information so that a user can understand what stresses orpotential dielectric breakdown a particular insulator is experiencing.The time scale or number of times that a current measurement may bemeasured may be in the range of 100ths of a second (milliseconds) to1000ths of a second (microseconds). Durations of an electrical pulse maybe in the range from approximately 1/10th of a second to approximately1/60th of a second. Each current measurement may be in 100ths of an amp(milliamps) to 1000ths of an amp (micro amps), or larger or smaller. Inaccordance with the present teachings, each current measurement isdisplayed graphically to allow a user, such as an electrical worker orlineman, to interpret a current measurement, but such measurements arealso recorded by the method or process of software within meter 10 by amemory 44, such as a hard drive or similar data memory device. Themeasurements of current and their duration may be stored in memory 44 ofthe meter 10 as a series of integers (or values) over a given timeperiod. As measurements of current are recorded by an analog currentsensor within ADC 16 and digitally converted, a process or method ofsoftware analyzes the current value or reading of the electrical pulsesand tracks both, the frequency and intensity. The frequency may be thenumber of current spikes for a given period of time, and the intensitymay be the amplitude or current value. These values are logged (e.g.stored) by the software. The time scale of the frequency of the pulsesis not displayed to the worker but is tracked by the software. Theworker is only shown the amplitude (the electrical current value) of thepulses. For a voltage of a DC power line 62 applied to a given insulator(e.g. boom 20 of bucket truck, ladder 70, or other live line tool) aknown, safe threshold value has been determined through experimentation.

Continuing with FIG. 2, various zones are evident on graphical display42 to display current values. For example, a safe (e.g. green) level ofcurrent is graphically displayed by a series of green bars on the meterwith a given value. Such a green zone is predetermined by the DC voltageclass (e.g. a DC voltage range) of DC power line 62. Thus, safe zones ofmeasured current by meter 10 will vary based upon the DC voltage rangeor precise DC voltage of a power line to which meter 10 is connected formeasuring current values “leaking” through insulating tools. Thus, anycurrent values or pulses below a predetermined value are showngraphically with green bars on a lighted vertical intensity graph. Thiscould also be displayed through colored lights, a physical graph, or anyother graphical display of intensity. Yellow zone (i.e. caution) or redzone (i.e. danger and stop working on DC power line 62) currentthreshold values are also displayed, but these may be accompanied by anaudible or visual warning signal of some type to alert the operator tothe presence of increasing intensity of these current pulses. Yellowzone current pulses are of value because changes in the physicalpositioning of the bucket, insulating properties or momentary voltageincreases on DC power line 62 may cause transient current spikes to bemeasured by meter 10. These must be noted and a user or worker must bealerted to yellow zone current pulses but they do not necessarilyconstitute a dangerous situation. Red zone current pulses indicate thata safe current threshold of the insulation integrity has been exceededor is imminent and any workers must remove themselves or the live linetool (e.g. boom 20) from the energized source, such as DC power line 62.Any red zone current pulses would be several orders of magnitude belowthe actual flashover threshold of the insulating live line tool (e.g.boom 20) to provide additional warning time and an adequate safetyfactor. A flashover is a dielectric failure of a device such as aninsulating live line tool (e.g. boom 20) that can also be thought of asthe creation of an instantaneous conductive path for discharge ofcurrent, or electrons, through the insulated device.

Because of the relatively large quantities of data the software willgenerate, in the form of current measurements or calculations, any “old”recorded and displayed current spikes may be constantly deleted from thememory in order to provide the user or worker with newer, more relevantdata as to the present or instantaneous insulating properties orcondition of an insulating live line tool (e.g. boom 20). As an example,a timescale of one minute may be used such that the software would countthe current spikes for a given value of time, say 100 recorded currentvalues per second, or 6,000 per minute. As the meter continues operationfor however many minutes or hours the meter is employed for a given timeof monitoring current, the oldest values of current measured or recordedmay be deleted and the graphical display may be reset to show thecorresponding lack of incidents, in the current time scale.

As an example, at time 1, which may be a first measurement of a currentthrough a boom 20 or other live line tool, a yellow zone currentmeasurement was recorded and displayed on the graphical display.Subsequently, the next 6,000 instances of current measurements throughthe boom 20 or other live line tool, no other yellow zone current spikesare measured. As a result, the software may be written to delete the6000 measurements, and the measurement at time 1, from memory 44.Moreover, the corresponding graphical representation on graphicaldisplay 42 of this current spike may be removed. If results are beingdisplayed on LCD display 40 in a continuous fashion, such display on LCDdisplay 40 may be removed. With memory deleted, the process may beginagain. Memory 44 may be used to plot graphs of current measurements overtime for specific DC voltages and each of the variety of insulatingdevices with which meter 10 will be used. Alternatively, no memory maybe utilized, and one or more of graphical display 42, LCD display 40,and an audible alarm for a yellow zone or red zone event may beutilized.

FIG. 10 depicts a flowchart 132 of an example routine controlled bysoftware within microcontroller 18, for example, to monitor currentthrough an insulating body such as boom 20, hot stick 92, 94, or ladder70, as examples, using meter 10 in accordance with the presentteachings. What is being monitored by the routine of flowchart 132 isthe flow of current, such as capacitive current. At step 134, theroutine may include providing a direct current (DC) power line to supplydirect current to a dielectric material. At step 136, the routine mayinclude detecting a direct current amperage value passing through thedielectric material. At step 138, the routine may include measuring thedirect current amperage passing through the dielectric material todetermine an instantaneous direct current amperage value. At step 140,the routine may include comparing the instantaneous direct currentamperage value to a known acceptable direct current amperage amplitudevalue. At step 142, the routine may include sounding an audio alarm whenthe instantaneous direct current amperage value is greater than theknown acceptable direct current amperage amplitude value. At step 144,the routine may include repeating, for a predetermined number of times,measuring the direct current amperage passing through the dielectricmaterial to determine ongoing instantaneous direct current amperagevalues. At step 146, the routine may include averaging the ongoinginstantaneous direct current amperage values to determine an averagevalue of the instantaneous direct current amperage value for apredetermined period of time. At step 148, the routine may includecomparing the average value of the instantaneous direct current amperagevalues for a predetermined period of time, to a predetermined thresholdvalue of the instantaneous direct current amperage values indicative ofa direct current flashover value for the material. At step 150, theroutine may include displaying the instantaneous direct current amperagevalue for a predetermined period of time on a visible readout of adirect current portable meter. At step 152, the routine may includeselecting by hand, a DC voltage class using a DC voltage class switch onthe direct current portable meter. Additional steps of the routine offlowchart 132 are envisioned, including intervening steps of those stepsdepicted in FIG. 10.

The discussion of any reference is not an admission that it is prior artto the present invention, especially any reference that may have apublication date after the priority date of this application. At thesame time, each and every claim below is hereby incorporated into thisdetailed description or specification as an additional embodiment(s) ofthe present invention.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents.

The invention claimed is:
 1. An apparatus for monitoring DC current froman energized DC electrical power line during maintenance to said powerline, wherein during said maintenance an aerial lift platform isoperatively coupled to at least said power line, the apparatuscomprising: a DC current measuring device connectable in series betweenthe aerial lift platform and an earth ground during said maintenance tomeasure a momentary DC leakage current value from the energized DCelectrical power line for each of a plurality of millisecond or smallertime intervals; a digital memory to store said measured momentaryleakage current values measured by the DC current measuring device,wherein the apparatus is arranged to compare said measured momentaryleakage current values stored in said digital memory to a predeterminedthreshold current value indicative of a DC current flashover currentvalue for the aerial lift platform.
 2. The apparatus of claim 1, furthercomprising: a DC numerical display arranged to display the DC leakagecurrent measured by the DC current measuring device; and an audio alarmarranged to sound upon the DC current measuring device measuring athreshold DC current value.
 3. The apparatus of claim 2, wherein theapparatus is arranged to: calculate a moving average for said measuredmomentary leakage current values; compare the moving average to thepredetermined threshold current value; and sound the audio alarm whenthe moving average is larger than the predetermined threshold currentvalue.
 4. The apparatus of claim 1, further comprising: a manual DCvoltage class selector switch that is manually adjustable to coincidewith a DC voltage of the DC electrical power line.
 5. The apparatus ofclaim 1, further comprising: an automatic DC voltage class selectorswitch that automatically switches to coincide with a DC voltage of theDC electrical power line.
 6. The apparatus of claim 1, furthercomprising: a graphical display arranged to visually depict a level ofthe DC leakage current measured by the DC current measuring device. 7.The apparatus of claim 1, further comprising: an electrical inputcollector connectable to the aerial lift platform; an analog front endarranged to measure amperage flowing from the aerial lift platform viathe electrical input collector; and, an analog to digital converterconnecting the analog front end to a microcontroller and being arrangedto convert an analog measurement from the analog front end to a digitalrepresentation for processing by the microcontroller.
 8. The apparatusof claim 7, wherein the analog front end comprises: one or more shuntresistors creating a path to the earth ground; one or more highbandwidth and high gain amplifiers arranged to measure potentialdifference across the one or more shunt resistors with reference toground earth, the potential difference corresponding to a leakagecurrent.
 9. The apparatus of claim 8, wherein the one or more highbandwidth and high gain amplifiers are configured for bi-directionalleakage current detection for a scale of +/−0 to 500 microamperes range.10. The apparatus of claim 8, wherein the one or more high bandwidth andhigh gain amplifiers are configured for single-ended leakage currentdetection for a scale of +/−0 to 1000 microamperes range.
 11. Theapparatus of claim 7, wherein the analog front end comprises: a Halleffect sensor arranged proximate to an electrical circuit component ofthe analog front end with a connection to the earth ground, the Halleffect sensor being arranged to detect a magnetic field of theelectrical circuit component, the magnetic field corresponding to aleakage current.
 12. A method for monitoring DC current from anenergized DC electrical power line during maintenance to said powerline, wherein during said maintenance an aerial lift platform isoperatively coupled to at least said power line, the method comprising:connecting a DC current measuring device in series between the aeriallift platform and an earth ground during said maintenance; measuring, bysaid DC current measuring device, a momentary DC leakage current valuefrom the energized DC electrical power line for each of a plurality ofat least millisecond time intervals; storing said measured momentaryleakage current values measured by the DC current measuring device asdata in a digital memory; and, comparing said measured momentary leakagecurrent values stored in said digital memory to a predeterminedthreshold current value indicative of a DC current flashover currentvalue for the aerial lift platform.
 13. The method of claim 12, whereinthe step of measuring further comprises: measuring every 1/60^(th) of asecond, the DC momentary leakage current.
 14. The method of claim 12,wherein the step of measuring further comprises: measuring every1/120^(th) of a second, the DC momentary leakage current.
 15. The methodof claim 12, further comprising: sounding an audible alarm when any ofsaid measured momentary leakage current values measured by the DCcurrent measuring device is larger than the predetermined thresholdcurrent value.
 16. The method of claim 12, further comprising:activating a visible alarm when any of said measured momentary leakagecurrent values measured by the DC current measuring device is largerthan the predetermined threshold current value.
 17. The method of claim12, further comprising: calculating a moving average for said measuredmomentary leakage current values; comparing the moving average to apredetermined threshold current value indicative of a DC currentflashover current value for the aerial lift platform; and sounding anaudible alarm when the moving average of said measured momentary leakagecurrent values measured by the DC current measuring device is largerthan the predetermined threshold current value.
 18. The method of claim17, wherein the step of calculating a moving average for said measuredmomentary leakage current values further comprises: calculating a movingaverage using a predetermined number of momentary leakage current valuesmeasured in succession by the DC current measuring device by excludingthe first momentary leakage current value of a series of momentaryleakage current values and including the next momentary leakage currentvalue following an immediately prior subset of momentary leakage currentvalues used to calculate an average.
 19. The method of claim 12, whereinthe step of storing comprises storing said measured current valueshaving up to a predetermined age in the digital memory and deleting saiddata over said predetermined age.